The EPA issued an "Endangerment Finding" which stated that greenhouse gases may “reasonably be anticipated to endanger public health or welfare."
Then the agency issued a rule to set limits on greenhouse gas emissions from cars and light trucks and another rule to set limits on stationary sources such as coal-fired power plants.

In the face of challenges from the energy industry and several states, the per curiam decision from the DC Circuit strongly backed the EPA's authority to issue the rules under the Clean Air Act.
The ruling noted that the U.S. Supreme Court determined in Massachusetts v. EPA that greenhouse gases can "unambiguously" be regulated as air pollutants.